| Type of Steel | Name | JIS (Japan) | AISI/SAE (USA) | DIN (Germany) | GB (China) |
|---|---|---|---|---|---|
| Low carbon (steel bar) | Round steel bar | SS400 (5541) | A36 | – | Q235 |
| Low carbon steel | S15C | SAE 1015 | CK15 (1.1141) | 15 | |
| S20C | SAE 1021 | CIC20 (1.0402) | 20 | ||
| Medium carbon steel | Medium carbon steel | S45C | SAE 1045 | CK45, C45 (1.0503) | 45 |
| S50C | SAE 1050 | CK50 (1.1213) | 50 | ||
| S55C | SAE 1055 | CK55 (1.1203) | 55 | ||
| Cr-Mo alloy steel | Round steel bar | SCM415 (SCM21) | – | 15CrMo5 (1.7262) | 15CrMo |
| Round steel bar | SCM420 (SCM22) | – | 25CrMo4 (1.7218) | 20CrMo | |
| Round steel bar | SCM440 (SCM4) | SAE 4140 | 42CrMo4 (1.7225) | 42CrMo | |
| Ni-Cr-Mo alloy steel | Round steel bar | SNCMno (SNCM21) | SAE 8620 | 21NiCrMo2 (1.6523) | 20CrNiMo |
| Round steel bar (with high nickel content) | SNCM420 (SNCM23) | SAE 4320 | 20CrNi2Mo | ||
| Round steel bar | SNCM439 (SNCM8) | SAE 4340 | 40NiCrMo6 | 40CrNiMo4 | |
| Pinion steel | _ | 17CrNiMo6 18CrNiMo7-6 | _ | ||
| Al-Cr-Mo alloy steel | Round steel bar | SACM645 (SACM1) | SAE 7140 | 41CrAlMo7 (1.8550) | 38CrMoAl |
| High-carbon chromium alloy steel | Bearing steel | SUJ2 | 52100 | (110Cr6 .30505) | GCr15 |
| Alloy tool steel | Cold work tool steel | SKD11 | D2 | X165CrMoV12 (1.2601) | Cr12MoV |
| Hot work tool steel | SKD61 | H13 | X40CrMoV51 (1.2344) | 4Cr5MoSiV1 | |
| High-speed steel | SKH51 (SKH9) | M2 | 56-5-2 (1.3343) | W6Mo5Cr4V2 | |
| Carbon tool steel | Round steel bar | SK 2 (SK 120) | W1-111/2 | – | |
| SK 3 (SK 105) | W1-10 | C1051,V1 (1.1545) | – | ||
| Stainless steel | 303 stainless steel | SUS303 | A1SI 303 | Xl2CrNi5188 (1.4305) | 1Cr18Ni9MoZr |
| 304 stainless steel | SU5304 | AISI 304 | X5CrNi189 (1.4350) | OCr181119 | |
| 316 stainless steel | SUS316 | AISI 316 | X5CrNiMo1810 (1.4401) | OCr17Ni1Mo2 |
Steel is one of the most widely used engineering materials due to its versatility, strength, durability, and ability to be alloyed and heat-treated for a wide range of applications. Its properties depend on chemical composition, heat treatment, and processing.
Key Properties of Steel
1. Mechanical Properties
| Property | Description |
|---|---|
| Tensile Strength | Resistance to breaking under tension. Ranges from 250 MPa (mild) to 2000+ MPa (tool steels). |
| Yield Strength | The stress at which steel begins to deform plastically. Important for load-bearing. |
| Hardness | Resistance to indentation or abrasion (measured in HRC, HB, HV). |
| Toughness | Ability to absorb energy and deform without fracturing (impact resistance). |
| Ductility | Ability to stretch without breaking. Indicated by elongation %. |
| Fatigue Strength | Resistance to repeated loading cycles. Essential for gears, shafts, and other components. |
2. Physical Properties
| Property | Typical Value or Range |
|---|---|
| Density | ~7.85 g/cm³ |
| Melting Point | ~1370–1510°C (depends on alloy content) |
| Thermal Conductivity | 45–60 W/m·K (lower for alloyed steels) |
| Electrical Conductivity | Poor (resistive metal) |
| Thermal Expansion | ~11–13 µm/m·°C (varies by grade) |
3. Chemical Composition (Basic Types)
| Steel Type | Main Alloy Elements | Notes |
|---|---|---|
| Carbon Steel | Iron + Carbon (up to 2%) | Most common. Classified as low (≤0.3%), medium (0.3–0.6%), and high carbon (0.6–1%). |
| Alloy Steel | Cr, Ni, Mo, Mn, V, etc. | Enhanced mechanical properties and heat resistance. |
| Stainless Steel | Cr ≥ 10.5% | Corrosion-resistant. Grades like 304, 316. |
| Tool Steel | W, Mo, Cr, V, Co | Used for cutting tools and dies. High hardness & wear resistance. |
| Maraging Steel | Ni, Mo, Co, Ti | Very high strength, low carbon, used in aerospace. |
4. Heat Treatment and Effects
| Process | Result |
|---|---|
| Annealing | Softens steel, improves ductility, and enhances machinability. |
| Quenching | Hardens steel (especially high-carbon/alloy steels). |
| Tempering | Reduces brittleness after quenching and balances hardness and toughness. |
| Normalizing | Refines grain structure, improves strength and toughness. |
| Case Hardening | Hardens the surface only (carburizing, nitriding). Ideal for gears and shafts. |
Common Steel Grades and Uses
| Grade | Type | Properties & Applications |
|---|---|---|
| AISI 1018 | Low-carbon | Good weldability, used for shafts and light-duty parts. |
| AISI 1045 | Medium-carbon | Stronger than 1018, suitable for gears, axles, and bolts. |
| SCM440 / 4140 | Alloy steel | High strength, wear-resistant, used in tools, gears, and structural parts. |
| SKD11 / D2 | Tool steel | High hardness and wear resistance, used in dies and cutting tools. |
| SUS304 | Stainless | Non-magnetic, corrosion-resistant, general-purpose SS. |
| SUS316 | Stainless | Better corrosion resistance (chlorides), used in marine/chemical. |
Selection Tips
Use low-carbon steel for welding and forming parts.
Use medium- to high-carbon or alloy steel for structural and load-bearing components.
Use stainless steel for corrosion resistance.
Use tool steel where wear resistance and hardness are essential.
Always consider heat treatment state — a steel in annealed condition behaves very differently from the same grade that is quenched and tempered.
Steel Grade Comparison Table
| Property / Grade | SCM440 (AISI 4140) | S45C (AISI 1045) | SUS304 (AISI 304) | SKD11 (D2 Tool Steel) | SUS316 |
|---|---|---|---|---|---|
| Type | Alloy Steel | Medium Carbon Steel | Austenitic Stainless Steel | Cold Work Tool Steel | Austenitic Stainless Steel |
| Carbon (C) | ~0.40% | ~0.45% | ≤ 0.08% | ~1.5% | ≤ 0.08% |
| Chromium (Cr) | ~1.0% | — | ~18% | ~12% | ~16–18% |
| Nickel (Ni) | — | — | ~8% | — | ~10–14% |
| Hardness (after HT) | 28–45 HRC | 20–30 HRC (quenched/tempered) | ~90–95 HRB (annealed) | Up to 60 HRC (after hardening) | ~90 HRB (annealed) |
| Tensile Strength | 850–1000 MPa (HT) | 600–800 MPa (HT) | ~520 MPa | ~1900 MPa (HT) | ~500 MPa |
| Weldability | Fair | Good | Excellent | Poor | Excellent |
| Machinability | Good | Good | Fair | Poor–Fair | Fair |
| Corrosion Resistance | Low | Low | High | Low | Very High (marine-grade) |
| Typical Applications | Gears, shafts, bolts, dies | Shafts, pins, gears | Food-grade tanks, piping | Punches, dies, and cold forming tools | Marine, chemical, pharma |
Summary by Use Case
SCM440 (4140): Great all-around high-strength steel for gears, shafts, and automotive parts — balances strength, toughness, and hardenability.
S45C (1045): Economical, suitable for general mechanical parts; not as hardenable as SCM440.
SUS304: Food-safe, rust-resistant; ideal for indoor corrosion-prone environments.
SUS316: Better for chloride-rich or marine environments, like coastal machinery or chemical tanks.
SKD11 (D2): Extremely hard and wear-resistant; not weldable; used for dies and industrial cutting.